1. Field of the Disclosure
The present disclosure relates to a device structure of an avalanche photodiode.
2. Discussion of the Background Art
An avalanche multiplier photodiode (avalanche photodiode: APD) as a highly-sensitive light receiving device has been widely introduced in, for example, an optical communication system using a photocarrier in a long wavelength range (1.5 micron band). A typical APD device operated in the long wavelength range is of a hole-injection type in which InP is an avalanche multiplier layer and usually has a structure in which an avalanche multiplier region is specified by a pn junction formed by Zn thermal diffusion to InP and a guard ring is disposed around the junction surface.
Meanwhile, it is assumed that in terms of rapidity and avalanche excess noise characteristics, an electron-injection type APD in which InAlAs is an avalanche multiplier layer is more advantageous than the hole-injection type APD in which InP is an avalanche multiplier layer. In InAlAs, since the ionization coefficient ratio between the electrons and the holes is larger, avalanche excess noise is low, and, in addition, since a gain-band product (GB product) increases, InAlAs has receiver sensitivity more excellent than that of InP-APD.
However, in an element manufacturing technical standpoint, a so-called “guard ring technique” for suppressing edge breakdown around a junction does not reach completeness in the hole-injection type. One reason for this is that it is difficult to form an “ion-injection type guard ring structure” usually used in the hole-injection type.
Thus, a structure alternative to the ion-injection type guard ring has been proposed. For example, there have been reported a structure (for example, see Non-Patent Documents 1 and 2) that avoids an influence of an edge electric field on an avalanche multiplier layer without forming an intended guard ring and a structure (for example, see Patent Document 1) where an embedded n-electrode having a low concentration is provided in a lower portion of an avalanche multiplier layer.